It is possible to search for collections of speeches in a variety of ways. The main subject terms for speeches are "speeches, addresses" and/or "oratory" (although "oratory" may retrieve discussions of rhetorical style as well as speeches). These may be combined with people (e.g., Lincoln), topics (e.g., civil rights), or various groups (e.g., women).
Useful Series: "Great Speeches Series" (Streaming video)
Potentially Useful Library of Congress Subjects for Rhetoric & Speeches
This Library of Congress Classification Outline holds true for any library in the world using the LC system. For example, American History will be classed in the Es & Fs. Classical Rhetoric & Oratory will often be classed in the PAs (Classical languages & literatures).